Conscientiousness

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For their 75-year study of 300 engaged couples who enrolled in the study in their mid-20s, researchers found that men who were seen by their friends as more conscientious — meaning that they were less likely to take risks but also tended to be more thorough and efficient — lived longer.

Participants in the study picked a handful of friends to rate their personality using a 36-question scale created by psychologist E. Lowell Kelly in 1940. To verify that it was still valid, the researchers recently compared it with several other personality tests from the past decade.

Questions in the scale ranged from general queries like "Is he physically energetic and peppy?" to more personal ones like "How does he meet his appointments?"

Of the men in the study, those who were seen as more conscientious lived longer. A 2007 study of Californian men and women between 1930 and 2000 came to similar conclusions. People — regardless of their gender — who were independently ranked as conscientious as children and as adults lived longer than their peers who were not conscientious during either phase of their lives.

Openness

For that same 75-year study, openness also emerged as a trait that was linked with a long life, second to conscientiousness. Men who ranked highly in terms of this quality — meaning that they were willing to lend an ear to new and different ideas, feelings, and concepts — tended to live longer than other men in the study.

A 2006 study of Japanese people aged 100-106 also suggested that openness was linked with longevity. "We speculate that in the oldest-old, higher imaginativeness and openness to new experiences would help them to adapt to the many losses (friends, family, health, function) that occur in advanced age," the researchers write in their paper.

Emotional stability

The 75-year longevity study had slightly different takeaways for women than it did for men — of the female participants in the study, emotional stability was the trait with the strongest links to a long life. This could be partially because when the study began, in the 1930s, women tended to be portrayed as highly emotionally unstable, and as a result being emotionally stable could have been linked with greater benefits for women than for men.

But, since that study looked only at people who'd already made it into ripe old age, it's tough to say whether or not the study participants developed these characteristics as a result of old age or if the traits helped them to live as long as they had.